1. Field of the Invention
The present invention relates to a kneading and extruding machine which includes a screw type two-shaft kneader and a gear pump for kneading, melting and extruding resin material. More particularly, the present invention relates to improvements in a kneading and extruding machine for extruding resin material melted in a uniform condition.
2. Background
In general, large-scale kneading and extruding machines for kneading, melting and extruding resin material are used in order to increase the processing capacity and enhance the efficiency of energy to drive the machines. In each large-scale kneading and extruding machine, a screw type two-shaft kneader for kneading and melting resin and a gear pump for extruding resin are combined. Concerning the screw-type two-shaft kneader, in order to prevent the occurrence of damage to the screw and cylinder when they come into contact with each other, both end portions of the screw, that is, the drive side and the front end side of the screw are rotatably supported. Concerning the gear pump, in order to reduce the overall height, the gear pump is connected onto the side the cylinder at the end of the screw type two-shaft kneader.
For example, as shown in the first drawing of Japanese Examined Patent Publication No. 6-31135, the conventional kneading and extruding machine includes the following structure. In FIGS. 8 and 9, reference numeral 1 is a screw type two-shaft kneader. The screw type two-shaft kneader 1 includes a cylinder 2 horizontally arranged, and two screws 3 rotatably inserted into an inner hole 2a formed in the cylinder 2. In the cylinder 2, there are formed a supply port 2b on an upper surface at the rear end portion of the inner hole 2a, a vent hole 2c on an upper surface of the middle portion, and a discharge port 2e arranged on one side of the end portion. The section of the inner hole 2a perpendicular to its axis is formed into two circles arranged horizontally. The two circles are adjacent and communicated with each other at the adjoining portion. At the end portion of the inner hole 2a, there is formed a discharging passage 2d from the adjoining portion to the discharge port 2e along the lower side of the inner hole 2a. The two screw shafts 3 are rotatably supported by bearings 4 arranged at the front and the rear end portion of the inner hole 2a. In the two screw shafts 3, there are provided flights by which resin material is successively conveyed, kneaded, deaerated and measured from the rear to the front end portion of the inner hole 2a. At the discharging section arranged at the front end portions of the screws 3, there are provided scraping flights 3c which are linearly arranged in the axial direction of the screws 3. In this connection, diameters of the flights of the screw 3 are the same, and in this embodiment, two series of flights are formed. In this conventional example, between the kneading section and the deaerating section, there is provided a gate type kneading degree adjusting device 5 for adjusting a clearance between the inner hole 2a of the cylinder 2 and the groove bottom of the screw 3, that is, for adjusting a sectional area of the flow passage of resin material. The discharge port 2e is connected with a gear pump 7 via a diverter valve 6.
The above kneading and extruding machine operates as follows. Resin material is supplied from the supply port 2b into the screw type two-shaft kneader 1. While the supplied resin material is being heated by a heating unit (not shown) via the cylinder 2 and melted and kneaded by the shearing action of the screw 3, the rear end portion of which is rotated by a drive unit (not shown), the resin material flows toward the discharging section. The flowing direction is changed by an angle of 90.degree. in the discharging section. Then the resin material is discharged from the discharging port 2e to the gear pump 7 via the diverter valve 6. After that, the pressure of the resin material is increased by the gear pump 7, and the resin material is extruded from the gear pump 7. During the above operation, the degree of kneading of the resin material is adjusted by the kneading degree adjusting device 5, and volatile components and water are removed from the resin material via the vent hole 2c. The diverter valve 6 is used when the melted resin material discharged from the screw type two-shaft kneader 1 is changed over between the conveyance to the gear pump 7 and the discharge to the outside of the apparatus. In the initial stage of operation, or in the change in resin material, the resin material that contains mixtures is discharged to the outside of the apparatus by the action of the diverter valve 6.
Since the conventional kneading and extruding machine is arranged as described above, the following problems may be encountered.
In the kneading and extruding machine of the present invention, it is important to extrude melted material of a uniform degree of kneading, that is, it is important to extrude melted material of a uniform resin temperature. In the screw type two-shaft extruder, resin material is equally melted and kneaded by the two screws when the resin material is conveyed from the supply port to a position immediately before the discharging section. Therefore, the resin material flows into the discharging section under the condition that the kneading degree and the melting temperature are uniform. However, since the discharging port is formed on one side of the cylinder in the discharging section, the shapes of the inner hole of the cylinder and the discharging passage are not the same with respect to the two screws arranged on the right and left. Accordingly, the resin material conveyed by one of the screws reaches the discharging port under a different condition from that of the resin material conveyed by the other screw. Specifically, when the resin material is discharged from the discharging section while the flowing direction is changed, the resin material is subjected to a shearing action by the flights between the discharging section and the inner hole of the cylinder. In this case, the rotational angle (the action distance) of the screw 3 subjected to the shearing action is different. As shown in FIG. 9, the rotational angle of the left screw 3a subjected to the shearing action is .theta..sub.1, and the rotational angle of the right screw 3b subjected to the shearing action is .theta..sub.2 (.theta..sub.1 &gt;.theta..sub.2) When the left screw 3a and the right screw 3b are rotated in a different direction, that is, when the left screw 3a is rotated clockwise and the right screw 3b is rotated counterclockwise, it is known that the resin material discharged from the left screw 3a flows on a lower layer in the discharge passage 2d, and that the resin material discharged from the right screw 3b flows on an upper layer in the discharge passage 2d. The resin material on the lower layer and the resin material on the upper layer, the viscosity of which is high in the melting condition, are seldom mixed with each other. Therefore, the resin material on the lower layer and the resin material on the upper layer flow while the layers are maintained in the previous condition. Accordingly, on the section of the flow of resin at the discharging port, the degree of kneading, that is, the melting temperature is locally different. Even after the layers of resin have been sent to the gear pump, they are not mixed. That is, under the condition that the layers are not made to be uniform, they are extruded. Even in a granulating device (not shown in the drawing) connected with the gear pump, the above condition is not changed. As a result, pellets of different physical properties, that is, pellets, the physical values of which fluctuate greatly, are produced.